Traditionally, commercial power from a utility has been used as the primary source of electrical power for a consuming entity, such as a telecommunications facility. Many power systems include backup power sources to deliver power in the event that the utility is unable to deliver power. Black-outs and other disturbances in the commercial power grid make this necessary.
To provide back-up, many facilities use an array of batteries. Operationally, if power from the commercial utility is lost, the battery array provides power during the time the commercial utility is out until the battery array is exhausted.
Prior power back-up systems would provide sufficient direct current (DC) back-up for the facility, but there is also a demand for supplying small amounts of alternating current (AC) back-up power to low load devices. Examples of these low load devices include facility lights, instrumentation, and cellular tower lights, which must be operational during power outages for safety purposes. Present battery back-up power systems for telecommunications facilities do not provide these lower AC power requirements.